This invention relates generally to the treatment of a hydrocarbon liquid such as crude oil or refined products to remove hydrogen sulfide and/or mercaptans therefrom. In an important aspect of the invention, the treatment involves the use of oil soluble amine scavengers. In another aspect, the invention relates to the use of nonregenerative scavengers to reduce the levels of H.sub.2 S and mercaptans in hydrocarbon liquid, particularly water-free hydrocarbon liquids.
Many crude oils and condensates contain naturally occurring components such as acid gases and mercaptans which must be removed or neutralized at some point in the producing, storage, or refining operations. The toxicity of hydrogen sulfide and mercaptans in hydrocarbon streams is well known in the industry and considerable expense and efforts are expended annually to reduce its content to a safe level. Many pipeline and storage regulations require pipeline hydrocarbon liquid to contain less than 4 ppm hydrogen sulfide. Some refined oils also contain reactive S such as H.sub.2 S and mercaptans and must be treated to lower the levels of their toxic substances.
Based on an article appearing in the Oil & Gas Journal, Jan. 30, 1989, nonregenerative scavengers for small plant hydrogen sulfide removal fall into four groups: aldehyde based, metallic oxide based, caustic based, and other processes. In the removal of hydrogen sulfide by nonregenerative compounds, the scavenger reacts with the hydrogen sulfide to form a nontoxic compound or a compound which can be removed from the hydrocarbon. As indicated above, the compounds useful in the method of the present invention are aldehyde type scavengers, specifically oil soluble scavengers.
Many of the aldehyde based scavengers form water soluble reaction products with H.sub.2 S, requiring the presence of water. For example, U.S. Pat. No. 4,978,512 discloses an H.sub.2 S scavenger comprising the reaction product of an alkanol amine comprising 1 to 6 carbon atoms with an aldehyde containing 1 to 4 carbon atoms. The reaction product forms a water-soluble lower alkyl hexahydro triazine, since the lower alkyl groups impart water solubility to the triazine. U.S. Pat. No. 4,748,011 discloses an H.sub.2 S scavenger for natural gas comprising an aldehyde (e.g. formaldehyde), a lower alkyl amine inhibitor and water (20-80%).
Oil soluble scavengers and suppressants are disclosed in the following patents and published applications:
(a) U.S. Pat. No. 2,783,205 discloses an acidic gas evolution suppressant for stabilized lubricating oils comprising the reaction product of a wide range of primary amines with a wide range of aldehydes, ketones, and ammonia. PA1 (b) U.S. Pat. No. 2,675,373 discloses an aldehyde H.sub.2 S evolution suppressant comprising aliphatic aldehydes and thiophene aldehydes. PA1 (c) U.S. Pat. No. 5,074,991 discloses an oil soluble, H.sub.2 S evolution suppressant comprising a diaminomethane compound. PA1 (d) European Patent Application 0405719A discloses an oil soluble imine compound which is the reaction product of an amine or polyamine and an aldehyde, dialdehyde or ketone. PA1 (e) European Patent Application 0411745A discloses an H.sub.2 S scavenger comprising the reaction product of an alkylene polyamine with formaldehyde.